The present invention relates to the field of the detection of an electric arc and, more specifically, to the detection and passivation of an electric arc in an on-board electrical device.
An electric arc may be generated where two contacts which initially conduct an electric current are separated. An electrical discharge, potentially reaching a temperature of 7000° C.-10,000° C., is then generated in the space between the two contacts, and maintains electrical conduction. The occurrence of sustained electric arcs over time in electrical storage, distribution and/or service elements may result in the deterioration of the electrical elements and adjoining equipment.
Accordingly, in order to guard against the risks of the propagation of electric arcs, it is important to detect the initiation of any electric arc in order to interrupt the electric circuit.
The detection of an electric arc is generally based upon the measurement of electric current intensity in the line supplying the electrical element. In practice, upon the occurrence of an electric arc, the current intensity rises significantly, and may exceed several times the rated current intensity.
However, in order to prevent any spurious tripping associated with false alarms, it is important to confirm the fault before any circuit interruption proceeds, thereby requiring a processing or confirmation time which, in many cases, is not compatible with the speed of propagation of the electric arc, which is of the order of 100 meters per second. The confirmation time may be several hundred milliseconds, or even several seconds, depending upon the current intensity and the temperature. These times are well in excess of those required for the extinction of the electric arc with no resulting damage to equipment and/or severe constraint thereupon.
In order to resolve problems of this type, insulating means are used for the protection of electrical elements and equipment against the risks of electric arc propagation during the confirmation time.
Specifically in the field of aeronautics, which is governed by particularly stringent constraints for safety and reliability, core electric systems and electrical distribution boxes in an aircraft are protected by a number of insulating and protective elements in order to prevent the propagation of any electric arcs between the various components or electrical elements.
In practice, the terminals of electrical elements are provided with double insulation, comprised of ceramic barriers and washers and specific surface treatments. For example, the double insulation of a retaining nut involves the surface treatment of the nut by the application thereto of an insulating material, and the addition of insulating washers with raised edges in order to inhibit the passage of an electric arc. In addition, mechanical protective structures such as grilles and/or covers are added in order to protect against small exterior metallic components or foreign bodies which might cause short-circuits.
Although highly effective, these types of protection have a number of disadvantages. Specifically, they complicate the installation, and increase both the dimensions and the mass of electrical distribution boxes. Moreover, grilles and other mechanical protective structures generate thermal stresses by restricting the exchange of heat between electrical devices and the exterior environment.